This is an epidemiologic study of 1458 human females exposed as fetuses to low doses of x-ray during maternal diagnostic procedures such as pelvimetry. For each study subject, an unexposed control is matched by hospital of birth, parity, and birthdate. All are black, born 1947- 1952 in Baltimore hospitals, and have remained in Baltimore. Our objective is to determine whether x-ray exposure during fetal life leads to changes that could be observed in the health and development of young adults, in their reproductive performance, or in their offspring. Phase I of this study, by ascertainment of registered Baltimore births to the study population, demonstrated a 10-15% increased fertility among exposed women. The difference remained after adjustment for economic, social, and medical factors. A non-significant increase in perinatal mortality was observed in babies of the exposed-in-utero women. Phase II, already started, is a direct follow-up of exposed-control pairs of women, now aged 21-27. Its purpose is to verify the differences in fertility found in Phase I, to uncover or rule out possible explanations for these differences unrelated to x-ray exposure, and to look for long term effects on the exposed individual herself, such as physical or mental retardation, impaired general health, or specific diseases, especially those related to the ovaries.